**The posted coordinates are great for parking near stage 1, but you need info at stage 2 (GC83M31) to find the bonus coordinates of the final location**
At stage 2, GC83M31 Rappelling proposal at N 42° 50.661′ W 112° 25.351′ inside that rappelling geocache you will find 3 coins. Those 3 coins can be placed on this picture below like the 3 missing pieces of a jigsaw. then you can read off the final coordinates as you follow the jumbled line.
There is parking at the AMI Kirkhead trailhead which is close to the final. You are looking for a large spray painted thermos tied to the base of a sage brush. It is only a short ways off the sandy hiking trail.
Terrain 5 rating is for the rappelling needed at GC83M31 to get the bonus info on the 3 coins.